Use venv for pre-commit in CI instead of pip install

The CI creates a venv via python_venv setup step that has pre-commit
installed from requirements.txt. Activate this venv instead of trying
to install pre-commit via pip which creates PATH issues.

This matches how the master branch script activates the venv before
running pre-commit hooks.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: nammn

scripts/evergreen/check_precommit.sh

@@ -6,16 +6,15 @@ initial_index_state=$(git diff --name-only --cached --diff-filter=AM)
 
 export EVERGREEN_MODE=true
 
-# Install pre-commit if not available
-if ! command -v pre-commit >/dev/null 2>&1; then
-  echo "Installing pre-commit..."
-  pip install pre-commit
-  # Add ~/.local/bin to PATH if it exists (pip installs scripts there)
-  if [[ -d "${HOME}/.local/bin" ]]; then
-    export PATH="${HOME}/.local/bin:${PATH}"
-  fi
+# Activate the venv if it exists (CI creates this via python_venv setup step)
+# The venv contains pre-commit installed from requirements.txt
+if [[ -f "venv/bin/activate" ]]; then
+  echo "Activating venv..."
+  # shellcheck disable=SC1091
+  source venv/bin/activate
 fi
 
+# pre-commit should now be available from the venv
 echo "Running pre-commit hooks..."
 echo "pre-commit version: $(pre-commit --version)"